it takes about 4 to 6 weeks for it to reach full effectiveness. It is better to take it earlier.

Of course it's better to take it earlier, but anyone who hasn't had it should still go get it. We have a LONG time before the end of flu season.

http://www.cdc.gov/flu/protect/keyfacts.htmDoes flu vaccine work right away?No. It takes about two weeks after vaccination for antibodies to develop in the body and provide protection against influenza virus infection.